The present invention concerns a computer device with a safety function for avoiding non-necessary disconnection of the computer device, comprising processor means, an ordinary memory unit connected to said processor means and arranged to comprise at least one program that is executed by the processor means, a supervisory unit that supervises the function of the computer device and that is arranged to, in case an error occurs, send a restart signal or a stop signal to the processor means.
Such computer devices are already known. The supervisory unit may for instance constitute a so-called “watchdog timer”. U.S. Pat. No. 4,763,296 describes the function of such a watchdog timer. Such a device thus has a timer that continuously is in operation when the computer device is used. If the timer reaches a predetermined value, i.e. if a predetermined time has elapsed, the watchdog timer generates a restart signal that causes a restart (reset) of the computer device. During normal use, the timer is set to zero at regular intervals by the normal program execution by the processor. In case an error occurs, for example if the computer executes an infinite subroutine, the timer will not be set to zero and the watchdog timer thus causes a restart of the system.
Also other kinds of computer devices with safety functions are already known. EP-A-481 508 thus describes a device that comprises a backup memory. When the current supply to the computer device is shut off, the status of the central processor and the content in a main memory are transferred to said backup memory. When then the computer device is started once again by again connecting the current supply, that which is stored in the backup memory will be restored.
EP-A-265 366 describes a computer device that comprises a primary memory and a backup memory. Switching from the primary memory to the backup memory is done by means of a “Backup Control System Transfer Mechanism”. This mechanism is relatively complicated. At the generation of a power-on-reset signal, said mechanism secures that restart is done from the primary memory (see column 6, lines 21–28).
There exists a need to improve the safety function of a computer device. There is thus a need of in a safe manner restarting the computer device when an error has been detected. Such an error that may cause errors in the operation of the computer is for example memory errors that may occur in the memory where programs that are executed in the computer device are stored. An error may also be caused by the software that is stored in the memory of the computer device. Such errors may for example occur when new software is used that has not been completely tested. Furthermore, there exists a need to secure the function of the computer device by relatively simple means. A further problem is to secure at least certain basic functions of the computer device when different errors occur.